show added/removed warnings in CI
scala compiler warnings only
addSbtPlugin("com.github.xuwei-k" % "sbt-warning-diff" % "version")
scala compiler warnings and scalafix warnings
addSbtPlugin("com.github.xuwei-k" % "warning-diff-scalafix-plugin" % "version")
https://github.com/xuwei-k/sbt-warning-diff/blob/49693f3e270f87e76/.github/workflows/ci.yml#L29-L70